Certain integration schemes require memory elements in the back-end-of-line (BEOL) to span large vertical distances and be formed in a column or pillar shape. For example, such memory elements are included in phase-change random-access memory (PCRAM), resistive random-access memory (RRAM or ReRAM), and magnetic random-access memory (MRAM) devices. Formation of these memory element pillars requires increasing metal hardmask vertical distance (e.g., thickness) to, for example, greater than 50 nm. The increased hardmask thickness leads to very high film stress (e.g., >200 MPa) and large wafer bow (e.g., >100 μm). Large wafer bow, in turn, leads to poor alignment to underlying features.
Accordingly, there is a need for improved techniques for forming hardmasks for pillar memory elements in BEOL applications.